Circuit breaker contact structure



Oct. 5, 1954 J. M. MILNE ET AL 2,691,086

CIRCUIT BREAKER CONTACT STRUCTURE Filed Feb. 7, 1952 Inventors: James M. Milne, Arthur- E. We're Their- Attorneg.

. tion.

Patented Oct. 5, 1954 UNITED STATES ATENT OFFICE CIRCUIT BREAKER CONTACT STRUCTURE Application February 7, 1952, Serial No. 279,314

4 Claims.

This invention relates to circuit breaker interrupting contact structure and, more particularly, to an improved combination finger type contact structure adapted effectively to confine the harmful efiects of arcing between separable contacts to a common secondary or arcing contact of an associated plurality of primary or currentmarrying contacts, both during opening and closing operations of the circuit breaker.

The formation of an arc at the coacting current-carrying surfaces of the contacts of a circuit breaker during an interrupting or closing operation of the breaker will result in the formation of high resistance oxides and sulfides and, especially in breakers of the liquid dielectric type, it is desirable to protect such surfaces by providing suitable arcing electrodes or tips across which the current is transferred during the initial opening movement.

This invention is particularly adapted for use in conjunction with circuit breakers of the type disclosed in Patent 2,164,175, issued to E. J. Frank on June 27, 1939, and assigned to the assignee of this invention; and is more specifically directed to providing the abutting type bridging contacts shown therein with rockable finger type contacts having arcing protection comparable to the arrangement'described and claimed in U. S. Patent 2,324,891 to Carl Thumim which is assigned to the assignee of this inven- While this invention is adapted for use in conjunction with circuit breakers .of the liquid blast type, the invention is not limited to such circuit breakers and is applicable to other types of breakers as well.

Thus, one object of this invention is to provide an improved combination primary and secondary contact structure for'high voltage circuit breakers which is compact in arrangement and efficient in operation.

Another object of this invention is the provision or an improved finger-type contact structure for cricuit interrupters in which arcing is concentrated at a point other than the main current-carrying surfaces so that the tendency for oxides and sulfides to be formed at such surfaces is minimized.

Still another object of this invention is to provide an improved contact structure for electric circuit breakers of the liquid blast type wherein the arcing electrode for a plurality of contact fingers is situated so that current transfer from the main current-carrying surfaces thereto is facilitated.

According to the invention, a circuit breaker having a fixed conducting element and a movable conducting element is provided with a unitary contact member pivotally mounted on one of said elements. The unitary contact member comprises an arcing contact portion and a current-carrying contact portion and cooperates with an associated pair of auxiliary currentcarrying contacts also pivotally mounted on said one element and arranged for limited movement relative to said unitary contact member, the auxiliary contacts being mounted for yieldable engagement with the other of said conducting elements.

For a better understanding of the invention, reference may be had to the following detailed description taken in conjunction with the accompanying drawing in which Fig. 1 is a perspective exploded view of a contact assemblage embodying the invention; Fig. 2 is a view of a portion of a circuit breaker embodying the invention with the moving contact thereof indicated by full lines in the act of separating and by dotted lines in an intermediate open position; Fig. 3 is a partial view of the same circuit breaker interrupter embodying the invention with the parts in the positions which they .00- cupy with the auxiliary contacts just making or breaking; and Fig. l is a partial view of the same circuit breaker embodying the invention with the various contact parts in the positions which they occupy when the breaker is fully closed.

With. reference to the drawing, a fixed conducting element l, assumed to be ailixed to the interrupter casing, is provided with a unitary contact member 2 which is adapted to cooperate with a movable conducting element 3 which, being one end of a reciprocable bridging contact as in the aforesaid Frank patent, is mounted on an insulating operating rod 4. The movable conducting element 3 is biased upwardly as by the contact pressure springs 5 and 6 against a shoulder member 1 disposed on the operating rod 4, whereby these springs are pre-stressed anticipatory to the upward motion of the rod 4 causing the movable conducting element 3 to contact the unitary contact member 2 under this spring load to complete a circuit across this region of the interrupter.

As will more clearly be seen from Fig. 1, the unitary pivotal contact member 2, which has .a conducting portion 33 and an arcing portion to, is provided with a pivot hole -8 of the same size as the corresponding aligned pivot holes 9 and it provided Within the fixed conducting .ele-

ment 1. When the contact member 2 is assembled in the fixed structure I, a pin H is inserted through these pivot holes so as to form a pivotal mounting for maintaining the combination main and arcing member 2 in position with its main body portion disposed within the pocket !2 formed in the fixed conducting element Projecting from opposite sides of the pivotal contact member 2 are a pair of spring-retaining arms I3 and I5 and another pair of shorter auxiliary contact-retaining arms l4 and I6 which cooperate in a manner which will be evident later. Provided in opposite sides of the fixed conducting member I are a pair of semi-cylindrical cavities which constitute pivotal anchorages aligned with holes 9 and iii to receive the cylindrically shaped end portions l9 and 20 of the auxiliary current-carrying finger contacts 2| and 22. Because these cavities are somewhat in excess of semi-cylindrical, as shown in the drawings, the fingers 2| and 22 are effectively anchored therein and cannot be displaced longitudinally therefrom; and, of course, they must he slipped into place from the side of the fixed conducting element I when assembling. Finger contacts 2| and 22 are respectively prevented from lateral movement in the assemblage by the retaining plates 23 and 24 which are secured to the fixed conducting element by screws 25 and 26. When assembled with contact 2 and its pin H in place, the auxiliary finger contacts 2| and 22 are arranged with respect to the central unitary contact member 2 so that contact 2| is captured for limited pivotal movement between the projections I3 and I4 while the contact 22 is similarly captured between the projections |5 and I6.

For the purpose of resiliently biasing contacts 2! and 22 downwardly from the arms l3 and |5 respectively, a pair of springs 21 and 28 are respectively interposed between the sockets 29 and 30 of the finger contacts and the projections I3 and I5; the latter having a spring guide post |3a as best seen in Fig. 3. From Fig. 1, it will be understood that the tips 3| and 32 of the finger contacts 2| and 22 are adapted to align with the current-carrying portion 33 of the unitary contact member 2 thereby to constitute a trio of adjacently disposed cooperating currentcarrying finger-type contacts. For ensuring that the auxiliary contacts 23 and 2| assume their proper share of the contacting load in the closed position, the abutments 42 of the contact member 2 permit the tips 3| and 32 of the auxiliary fingers to lie somewhat below the corresponding tip 33 of the central contact member 2 as best seen in Figs. 2 or 3. Thus, as the contact area 34 of the movable conducting element 3 moves up into closed contact position, the auxiliary fingers 2| and 22 resiliently yield into their final position of alignment with the central contact portion 33 against the bias of their individual contact springs 2'? and 28 supported from the extended arms of the central unitary contact 2.

The limiting position of unitary contact member 2 and its associated auxiliary fingers, when the breaker is opened, is determined by the shoulders 35 and 33 which are provided on the unitary contact member 2. Thus, the compressional spring 39 housed in a pocket 43 in the fixed conducting element and pressing into engagement with the arcing tip portion 43, urges the pivoted contact finger assembly counterclockwise with shoulders 35 and 36 in abutting engagement with the corresponding projections 4 31 and 38 formed on the fixed conducting element Since the finger contacts 2| and 22 as well as their contacting surfaces 3| and 32 and the contacting surface of the current-carrying contact 33 are all formed of good electrically conducting material such as copper, suitably silver faced or plated, these current-carrying contacts are not particularly adapted for resisting the damaging effects due to arcing. For assuming this burden, the downwardly projecting arcing tip of the unitary contact member 2 has an arcresistant facing 40 afiixed thereto in an appropriate manner and a corresponding arc-resistant facing 4| is affixed to the corresponding coacting surface of the movable conducting element 3. In Fig. 2, the solid-line conducting element 3 is shown in the position which this member transiently occupies as the contact 4| is about to separate to draw an are or, conversely, as it first engages the arcing tip 43. The dottedline position of the movable conducting member 3 in Fig. 2 is indicative of the open, or partially open, position of the breaker.

Fig. 3 is a view similar to Fig. 2 but with the parts of the contact arrangement in the positions they occupy at the instant when the current-carrying portion 34 of the movable conducting element 3 is about to separate from the finger contacts 2| and 22; and it will be observed, from Fig. 4, that the initial opening movement has already effected separation from the middle finger tip 33.

Considering the opening transition from Fig. 3 to Fig. 2; it will be noted that during the wipe of the arcing tips 40 and 4|, the assemblage comprising central contact 2 and side contacts 2| and 22 has been rotating counter-clockwise under the urge of spring 39 to close the gap between the corresponding abutments 36 and 31 while the moving bridging element 3 has been moving downward. In other words, the tips 3|, 32 and 33 of the trio of associated currentcarrying contact fingers actually have been moving upward, that is, away from the downwardly moving bridging contact. Such action ensures that an eifectively widening gap is rapidly forming between the primary contacts while current, under magnetic loop effect, is transferring to the shunting path through the arcing contacts. Thus, the burden of arcing is properly assumed by the arcing electrodes which are well removed from the primaries so that the current-carrying duties or the primaries are preserved for comparatively long operational periods.

During a closing operation of the breaker, the parts sequentially occupy the transient positions indicated in Figs. 2 and 3 and then ultimately establish conducting relationship among the several sets of cooperating contacting surfaces as shown in Fig. l, viz., with springs 5 and 6 urging the bridging element 3 into conducting engagement with tips 33 and 43 of the unitary pivotal central contact member 2, and with the individual springs 21 and 28 pressing the auxiliary contact fingers 2| and 22 into conducting engagement with the bridging element 3. Current is carried from the finger tips 3|, 32 and 33 to the fixed conducting element I through the reaction of these spring forces against the pivotal joints of the pivotal contact assemblage.

From the above description, it will be clear that we have provided a new contact arrangement wherein one finger-type pivotal currentcarrying contact is closely coupled to an associated current-carrying contact or contacts, and in which the one contact has integrally formed therewith a arcing electrode portion through which the current from the plurality of currentcarrying contacts is shunted during the circuitinterrupting operation. A further feature is that we have provided a master pivotal contact which when operated toward open or closed position, carries with it one or more accompanying resiliently-coupled auxiliary contacts for sharing the current-carrying duty of the main contact.

While we have illustrated and described a particular embodiment of our invention, we do not wish to be limited thereto and. intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A contact arrangement for an electric circuit breaker comprising a fixed conducting element, a movable conducting element, a unitary contact member pivotally mounted on one of said conducting elements and including an arcing contact portion and a current-carrying portion sequentially engageable and disengageable with the other of said conducting elements, a pair of spaced projections extending from said unitary member, a finger contact having one end thereof pivotally mounted on said one conducting element and having the other end thereof disposed between said projections, and spring means interposed between one of said projections and said finger contact for biasing said finger contact toward the other of said projections.

2. A contact arrangement for an electric breaker comprising a fixed conducting element, a movable conducting element, a unitary contact member pivotally mounted on one of said conducting elements and havin thereon an arcing contact portion and a current-carrying contact portion sequentially engageable and disengageable with the other of said conducting elements, separate pairs of spaced projections disposed on opposite surfaces of said unitary member, a separate finger contact disposed in the space between each pair of said projections, one end of each of said finger contacts being pivotally mounted on said one conducting element and the other end of each of said finger contacts lying adjacent said current-carrying contact portion, and spring means biasing said finger contacts in a direction generally toward said other conducting element.

3. A contact arrangement for an electric circuit breaker comprising a fixed conducting element, a movable conducting element, a unitary contact member pivotally mounted on one of said conducting elements and having thereon an arcing contact portion and a current-carrying contact portion sequentially engageable and disengageable with the other of said coductin elements, separate pairs of spaced projections extending from opposite sides of said unitary memher, a separate finger contact captured in the space between each pair of said projections, one end of each of said finger contacts being anchored within a cavity of cylindrical configuration formed in said conducting member, each of said cavities being transversely disposed with respect to its associated finger contact and being open along one side to receive the associated finger contact, said cavities and said one end of said finger contacts forming plug and socket pivots for said finger contacts, said plug and socket pivots being substantially coaxially disposed with respect to the pivotal mounting of said unitary contact member.

4. A contact arrangement for an electric circuit breaker comprising a fixed conducting element, a movable conducting element, a unitary contact member movably mounted on one of said conducting elements and including a pair of spaced projections extending therefrom, a finger contact having one portion thereof movably mounted on said one conducting element and another portion thereof disposed in the space between said projections, and springs means interposed between one of said projections and said finger contact for biasing said finger contact toward the other of said projections.

References Cited in the file of this patent UNITED STATES PATENTS 196,430 Great Britain Apr. 26, 1923 

